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Friday, November 7, 2014

Three things I learned about sutures

My desk on the day. Combine this with a good tutor and this is my idea of a productive day off.

Last week I attended a
workshop on suturing. Suturing, you ask? Isn’t that something you should know
already? Yep, and I’ve done it pretty much most days for the last ten years.
All the more reason to tweak and refine – a process which really shouldn’t end
(read more about developing surgical skills here).

Dr Ilana Mendels, founder of
VetPrac, thinks the same way. So she organised a half-day suture workshop. It
was attended by new and recent graduates – veterinarians one or less years out
of university – but also a range of experienced vets, with ten, twenty or more
years of practice.

Morning tea.

One thing many outsiders
don’t realise is that while employers provide some expenses for veterinary
continuing education, it’s often done on a vet’s day off, and at their own
expense. I’m a big believer – where possible – in investing in one’s own
education and training.

So our little group gathered under the tutelage of surgical specialist
Andrew Marchevsky, from the Small Animal Specialist Hospital. His surgical caseload is
incredible. He generally doesn’t find himself performing routine desexing
procedures, but tends to take on things like spinal surgery, radical oncologic
surgeries and skin reconstructions. And he’s not above obsessing about sutures.
In fact, that’s what makes him a great surgeon.

During the workshop, we were
provided with surgical instruments and an endless supply of different types of
suture material.

What did I learn?

Complications occur in the
best hands. Even with the best surgeons, the best instruments and the best
facilities, intestinal resection and anastomoses break down in at least 10 per
cent of cases – and that’s a statistic from the human medical field. Second
surgeries are not uncommon and – even where we think it is unlikely – we should
inform owners that this is a possibility.

In general, Australian
veterinarians at least use suture that is too thick. According to Dr Marchevsky,
we should be using finer suture – 3/0 in the gut, 4/0 for cats. He believes 2/0
is too thick for skin and ligatures in most cases.

The aim of skin sutures
should be for gentle apposition ONLY. There should be no tension and they
should be slightly lose when placed.

Suture materials are
categorised by the length of time it takes for 50 per cent of the original
strength to be lost. Bladder is the only tissue that returns to 100 per cent of
its original strength following surgery (14 days, in fact). Skin takes around
365 days to get to 70 per cent of its original strength.

Dr Marchevsky feeds animals
following intestinal surgery sooner rather than later. It was once argued that
animals should be fasted for at least 48 hours to prevent leakage of the surgery
site. That ignores the fact that around 1L of gastric juices are produced every
day and have to go somewhere. “They don’t leak because you feed them,” he said.

When closing the linea alba,
the less muscle you include in the sutures the better. The external fascia is
the tension holding layer and this should be the focus.

Dr Marchevsky is a big fan
of intradermal sutures and demonstrated his technique. He talked about the pros
and cons of different suture patterns and did some troubleshooting.

For the nerds out there, I
had also forgotten just how much physics and chemistry is involved in suture
design and production. And it was also a nice opportunity to review the history
of sutures. For example, absorbable sutures were introduced in the 1970s. These
days sutures are sterilised with gamma radiation or ethylene oxide, depending
on the material they’re made of.

Sutures are absorbed by
hydrolysis, leading to gradual disappearance of the thread over a particular
time.

We were taught to almost
uniformly avoid braided sutures because they cause tissue drag and potentially
a saw effect when they thread through tissue, but advances in coating such
materials mean this is a reasonable choice in some cases. Capillarity of the
suture is defined as the ease through which fluids can be wicked along the
thread…its present to high in multifilaments due to “the loose intersticies of
their fibres”, and monofilaments have no capillarity.

Braided suture is more
flexible and has less memory than monofilaments, making it easier to use.
(Memory is the capacity of the thread to return to its former shape. Thread
memory has an impact on the way we USE suture, ie if it has more memory it
likes to tie itself in knots spontaneously, which can frankly be a pain).

Knot security is determined
by knot fixation which depends on: thread stiffness, coffecient of friction,
elasticity and plasticity. According to the experts at B Braun, knots should
have at least three loops with 3mm long ends. Cutting down those “ears” to make
it neater isn’t helpful beyond the 3mm mark! What was interesting is that there
remains a lack of consensus about knots. According to the B Braun literature,
“it is commonly accepted that 4 knots are necessary for securing a braided
suture and 6-8 knots are required in the case of a monofilament suture”.

Knot tensile strength is
usually 30-50% less than the linear tensile strength of a suture – hence the
need to get it right.

Thread gauge is standardised
according to the European Pharmacopoeia decimal classification, although the
packets us the United States Pharmacopoeia classification.

USP

EP (Decimal)

Thread gauge in mm

5-0

1

0.10-0.149

4-0

1.5

0.15-0.199

3-0

2

0.20-0.249

2-0

3

0.30-0.349

0

3.5

0.35-0.399

1

4

0.40-0.499

From “Suture Glossary” – B
Braun

The diameter applies to both
needle AND thread. Suture glide describes how well the suture passes through
tissue, and, to throw some physics around “is a function of its coefficient of
friction”. Monofilaments have better glide.

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